The identification of rock types, also referred to as petrofacies, as a method of reservoir characterization is indispensable for accurate prediction of hydrocarbon production from subsurface reservoirs. Identifying petrofacies is an essential process for Pore to Core upscaling, which is a part of the combined reservoir characterization and predictive analysis (simulation) process. Pore to Core upscaling refers to the process of assigning petrophysical and hydraulic conductivity properties determined from pore scale measurements to a core, which would typically be used to describe subsurface rock types in the grid-cells of a reservoir simulation model. The petrofacies are used in conjunction with the disparate petrophysical and/or hydraulic properties to spatially characterize multiphase flow behavior in the cells of the 3D geocellular grid. Typically these petrofacies are derived using a priori derived seismic attribute, well log and core analysis data, which are analyzed on a cross-plot according to the disparate petrophysical and/or hydraulic properties. Standard practice is to plot relevant data points (e.g. permeability and porosity) in a cross-plot and define clusters of data using a linear relation. Not only does this practice limit the analysis to linear relationships, but it is also a user intensive selection process. Consequently, this practice impedes the use of quantitative and automated categorization methodologies that would facilitate streamlined reservoir characterization.